RESUMO
This study investigated the influence of angiotensin II, perfused into one common carotid artery at a dose of 0.065 micrograms/kg/min, on the cerebrovascular resistance of the anesthetized rabbit by means of complementary in vivo methods. Heat clearance and mass spectrometry measurements indicated that in the homolateral caudate nucleus angiotensin induced a significant decrease in local blood flow (18.2 +/- 9%), a fall in pO2 (14.2 +/- 5.3%) and no significant change in pCO2. The [14C]ethanol tissue sampling technique revealed a significant decrease in flow in all 10 structures sampled in the brain. This decrease was similar in magnitude in both the ipsilateral and the contralateral hemisphere with regard to the site of injection. When expressed in terms of cerebrovascular resistance (CVR) and allowing for a slight increase in blood pressure (less than 10%), these results show that angiotensin II infusion induced an increase in CVR of 18-32%. We conclude that: A unilateral intracarotid infusion of a low dose of angiotensin II induces an increased vascular tone in all cerebral structures. This action, being bilateral, cannot readily be explained by a direct action of angiotensin II on the cerebral vessels in view of the very low recirculating concentration of angiotensin II (less than 10(-9) M). The hypothesis of a cerebral vasomotor influence of angiotensin II by action on a central structure is discussed.
